Trimethyl(ethylcyclopentadienyl)platinum, process for producing the same and process for producing platinum-containing films with the use of the same

ABSTRACT

A Pt compound which is in the form of a liquid at room temperature for producing Pt films usable as electrode films in semiconductor devices by the CVD method; a process for producing the compound; and a process for producing films with the use of the same. 
     A novel compound trimethyl(ethylcyclopentadienyl)platinum (C 2  H 5  C 5  H 4 )Pt(CH 3 ) 3  is in the form of a liquid at room temperature and shows a sufficient vapor pressure at around 35° C. Thus, it can be quantitatively supplied by gas bubbling or with the use of a liquid mass flow controller as a feedstock in the CVD method and thermally decomposed on a substrate at 150° C. in a hydrogen atmosphere to give pure Pt films. This compound can be produced at a high yield by reacting iodotrimethylplatinum with sodium ethylcyclopentadienide in a solvent.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to trimethyl(ethylcyclopentadienyl)platinum (C₂H₅ C₅ H₄)Pt(CH₃)₃, a process for producing the same and a process forproducing platinum-containing films by the chemical vapor depositionmethod (hereinafter referred to simply as "the CVD method") by using thesame.

2. Description of the Prior Art

With the recent tendency toward ultra-large-scale integrated circuits(ULSI), studies are under way to develop (Ba, Sr)TiO₃ films having highdielectric constants, ferroelectric Pb(Zr,Ti)O₃ films, SrBi₂ Ta₂ O₉films, etc. as capacitors. Also, investigations are in progress on Ptfilms to be used as electrodes therefor.

Although it has been a practice to produce these Pt films by the Ptmetal sputtering method, it is expected that the desired step coverageor mass-productivity in further microscaled cases can be achieved by theCVD method. As the volatile Pt compounds to be used in the CVD method,investigations are in progress on trimethyl(cyclopentadienyl)platinum(C₅ H₅)Pt(CH₃)₃, trimethyl(methylcyclopentadienyl)platinum (CH₃ C₅H₄)Pt(CH₃)₃, cyclopentadienyl(allyl)platinum (C₅ H₅)Pt(C₃ H₅),dimethyl(cyclooctadiene)platinum (C₈ H₁₂)Pt(CH₃)₂,methyl(carbonyl)cyclopentadienylplatinum (C₅ H₅)Pt(CH₃)(CO),trimethyl(acetylacetonato)platinum (C₅ H₇ O₂)Pt(CH₃)₃,bis(acetylacetonato)platinum Pt(C₅ H₇ O₂)₂, etc. In addition, there areplatinum compounds containing phosphorus P, fluorine F or chlorine Cl.However, these compounds are omitted herein, since they are unfavorablein producing silicone semiconductors.

Y. J. Chen and H. D. Kaesz Appl. Phys. Lett., Vol. 53, 1591 (1988)!disclosed that starting with trimethyl (cyclopentadienyl)platinum (C₅H₅)Pt(CH₃)₃, a Pt film was formed on an Si substrate at 180° C. in ahydrogen atmosphere at 1 atm by the CVD method by sublimating thefeedstock from a source at 25° C. together with an Ar gas. The obtainedfilm was a bright one showing a high reflectance and being contaminatedwith not more than 1 atomic % of carbon, when examined by the XPSanalysis.

However, (C₅ H₅)Pt(CH₃)₃ has a melting point of 108° C. and, therefore,is in the form of solid crystals at room temperature. It shows a vaporpressure of 0.1 Torr and 1 Torr respectively at around 31° C. and 58° C.Thus, it is to be supplied by sublimation.

Z. Xue, M. J. Strouse, D. K. Shuh, C. B. Knobler, H. D. Kaesz, R. F.Hicks and R. S. Williams J. Am. Chem. Soc., Vol. 111, 8779 (1989)!disclosed that starting with trimethyl(methylcyclopentadienyl)platinum(CH₃ C₅ H₄)Pt(CH₃)₃, a Pt film was formed on an Si substrate at 120° C.by the CVD method by sublimating the feedstock from a source at 23° C.together with an Ar gas and simultaneously feeding a hydrogen gas into athermal decomposition chamber to give an atmosphere containing about 20%of hydrogen (1 atm). The obtained film was a bright one showing a highreflectance and being contaminated with not more than 1 atomic % ofcarbon, when examined by the XPS analysis.

However, (CH₃ C₅ H₄)Pt(CH₃)₃ has a melting point of 30° C. and,therefore, is in the form of solid crystals at room temperature. Itshows a vapor pressure of 0.1 Torr and 1 Torr respectively at around 30°C. and 56° C. Thus, it is to be supplied by evaporation or sublimation.Although trimethyl(methylcyclopentadienyl)platinum liquefies uponheating, it turns into the solid again when cooled to room temperature,which makes it necessary to provide countermeasure with respect toapparatus.

U.S. Pat. No. 5,130,172 has disclosed a process for coating a substratewith a metal comprising: maintaining the substrate at a temperature upto 190° C.; exposing this substrate to a vaporized organometalliccompound represented by the formula L_(n) MR_(m) obtained by heating toa temperature up to 100° C.; then exposing the substrate to hydrogen gasat a temperature up to 100° C.; and reacting the organometallic compoundwith hydrogen to thereby form a metal film. In the above formula L_(n)MR_(m), L is hydrogen, ethylene, allyl, methylallyl, butadienyl,pentadienyl, cyclopentadienyl, methylcyclopentadienyl, cyclohexadienyl,hexadienyl, cycloheptatrienyl or derivatives of these compounds eachhaving at least one alkyl side chain having less than five carbon atoms;M is a metal that can readily cycle between two oxidation states and cancatalyze hydrogenation of hydrocarbon ligands; R is methyl, ethyl,propyl or butyl; n is an integer from 0 to the valence of the metal; mis an integer from 0 to the valence of the metal; and m plus n mustequal the valence of the metal.

The Pt compounds given in the claims specifying the same aretrimethyl(cyclopentadienyl)platinum (C₅ H₅)Pt(CH₃)₃,trimethyl(methylcyclopentadienyl)platinum (CH₃ C₅ H₄)Pt(CH₃)₃,cyclopentadienyl (allyl)platinum (C₅ H₅)Pt(C₃ H₅),cyclopentadienyl(methylallyl)platinum (C₅ H₅)Pt(CH₃ C₃ H₄) andmethylcyclopentadienyl(methylallyl)platinum (CH₃ C₅ H₄)Pt(CH₃ C₃ H₄).

Among these compounds, those having melting points reported inDictionary of Organometallic Compounds, Vol. 3, (2nd Ed. 1996, Chapman &Hall), etc. are listed in Table 1.

                  TABLE 1    ______________________________________    Melting points of compounds                                     M.p.    Compound            Chemical formula                                     (° C.)    ______________________________________    trimethyl(cyclopentadienyl)platinum                        (C.sub.5 H.sub.5)Pt(CH.sub.3).sub.3                                     105    trimethyl(methylcyclopentadienyl)                        (CH.sub.3 C.sub.5 H.sub.4)Pt(CH.sub.3).sub.3                                      30    platinum    cyclopentadienyl(allyl)platinum                        (C.sub.5 H.sub.5)Pt(C.sub.3 H.sub.5)                                     63-64    dimethyl(cyclooctadiene)platinum                        (C.sub.8 H.sub.12)Pt(CH.sub.3).sub.2                                     94-95    methyl(carbonyl)cyclopentadienylplatinum                        (C.sub.5 H.sub.5)Pt(CH.sub.3)(CO)                                     <-20    trimethyl(acetylacetonato)platinum                        (C.sub.5 H.sub.7 O.sub.2)Pt(CH.sub.3).sub.3                                     solid    bis(acetylacetonato)platinum                        Pt(C.sub.5 H.sub.7 O.sub.2).sub.2                                     250    ______________________________________

As Table 1 shows, the compounds exceptmethyl(carbonyl)cyclopentadienylplatinum are each in the form of a solidat room temperature of 25° C. On the other hand,methyl(carbonyl)cyclopentadienylplatinum is unfavorable as a feedstockin mass production, since it has CO and shows a somewhat poor storagestability.

The supply of the starting compound by sublimation in the CVD method isinferior in quantitative supply, regulation and mass-productivity to theliquid supply system or evaporation supply system with the use of acarrier gas bubbling into the liquid. If the starting compound can beliquefied by heating, it can be supplied by evaporation and thus theregulation can be significantly improved. Even in this case, however,the systems and apparatuses usable therein are considerably restrictedas compared with the case where the starting compound can be handled inthe form of a liquid at room temperature. Accordingly, it is required toemploy a starting compound which is a liquid at room temperature andshows a sufficient vapor pressure after heating. However, there is nopublicly known compound which is usable in Pt film formation by the CVDmethod, is in the stable form of a liquid at room temperature of 25° C.and has a vapor pressure.

One of the problems to be solved by the present invention is to disclosea compound which is usable in Pt film formation by the CVD method, is inthe stable form of a liquid at room temperature of 25° C. and has avapor pressure and to provide a process for producing Pt films by theCVD method with the use of the compound. The present invention furtheraims at providing a process for producing the above compound.

SUMMARY OF THE INVENTION

The present inventor has been studying the synthesis of organometalliccompounds and the CVD method with the use of the same for a long time.To solve the above problems, he synthesized and purifiedtrimethyl(ethylcyclopentadienyl)platinum (C₂ H₅ C₅ H₄)Pt(CH₃)₃, which isan unknown compound, and measured the melting point and vapor pressurethereof. As a result, he revealed that this compound has favorablephysical properties. Then he formed Pt films by the CVD method with theuse of this compound and thus found out that stable and good films couldbe obtained thereby, thus completing the present invention. Accordingly,the present invention has been established based on the finding thattrimethyl(ethylcyclopentadienyl)platinum (C₂ H₅ C₅ H₄)Pt(CH₃)₃ is usableas the material which is a liquid at room temperature of 25° C. to beused in forming Pt films by the CVD method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The compound according to the present invention istrimethyl(ethylcyclopentadienyl)platinum (C₂ H₅ C₅ H₄)Pt(CH₃)₃.

The present invention further provides a process for producing the abovecompound which is excellent in mass-productivity. The process accordingto the present invention is derived from the method for synthesizingtrimethyl(cyclopentadienyl)platinum (C₅ H₅)Pt(CH₃)₃ disclosed by Y. J.Chen and H. D. Kaesz Appl. Phys. Lett., Vol. 53, 1591 (1988)! whichcomprises reacting iodotrimethylplatinum Pt(CH₃)₃ I in a toluene solventwith sodium cyclopentadienide Na(C₅ H₅) while stirring at a temperatureof -78° C. to room temperature, recovering and sublimating to givetrimethyl(cyclopentadienyl)platinum (C₅ H₅)Pt(CH₃)₃ at a yield of 52%based on Pt.

The present inventor has found out that the aimedtrimethyl(ethylcyclopentadienyl)platinum (C₂ H₅ C₅ H₄)Pt(CH₃)₃ can beobtained by effecting the same reaction as the one in the method ofKaesz et al. under the same conditions but using sodiumethylcyclopentadienide instead of the sodium cyclopentadienide.

After the completion of the reaction, the solvent is distilled off andthe slurry residue is distilled in vacuo (50° C./0.3 Torr) to give apale yellow liquid. By effecting Pt content analysis, CH analysis and ¹H-NMR analysis, this liquid is identified withtrimethyl(ethylcyclopentadienyl)platinum (C₂ H₅ C₅ H₄)Pt(CH₃)₃. Theobtained product has a melting point of not higher than -78° C. andtherefore is in the form of a viscous liquid without crystallization at-78° C. It has a viscosity of about 5 cp at room temperature.

It remains stable in the air and scarcely reacts with water. It has ahigh thermal stability. According to TG-DTA in an Ar atmosphere (1 atm),it is evaporated completely at 170° C.

The present invention further provides a process for producing highlypure trimethyl(ethylcyclopentadienyl)platinum (C₂ H₅ C₅ H₄)Pt(CH₃)₃usable in producing electronic materials.

The present invention further provides a process for producingplatinum-containing films by the CVD method with the use oftrimethyl(ethylcyclopentadienyl)platinum (C₂ H₅ C₅ H₄)Pt(CH₃)₃.

This compound is maintained at a temperature of from about 20 to 100° C.and a carrier gas is bubbled thereinto and evaporated together with thecompound. The resultant gaseous mixture is fed into a thermaldecomposition reactor, wherein it is thermally decomposed in a hydrogenatmosphere on a substrate at 100 to 300° C. to thereby form a Pt film.Instead of the evaporation feeding by bubbling, the compound may be fedand evaporated by using a liquid mass flow controller.

To produce films free from carbon or oxygen in the present invention, itis necessary to effect the thermal decomposition in a hydrogenatmosphere. Instead of the thermal decomposition method, the substratemay be irradiated with a XeCl eximer laser at 308 nm or argon ion lasersat 351 and 364 nm to thereby accelerate the decomposition.

EXAMPLE 1 Production of trimethyl(ethylcyclopentadienyl)platinum (C₂ H₅C₅ H₄)Pt(CH₃)₃

A four-necked flask (1 1) provided with a reflux condenser, athermometer, a dropping funnel and stirring blades was purged with argonin vacuo and then 600 ml of toluene was fed thereinto. Next, 34.5 g (94mmol) of iodotrimethylplatinum Pt(CH₃)₃ I was added thereto anddissolved therein. This reaction flask was cooled to -78° C. and 60 mlof a solution of 14.0 g (121 mmol) of sodium ethylcyclopentadienideNa(C₂ H₅ C₅ H₄) in THF was added thereto via the dropping funnel understirring. After stirring at -78° C. for 30 minutes, the mixture wasgradually heated to room temperature and then stirred at roomtemperature for 30 minutes. After distilling off the solvent underreduced pressure, a slurry was obtained. Then this slurry was subjectedto vacuum distillation at 0.3 Torr to give 16.1 g of a pale yellowliquid as a distillate fraction at 50 to 55° C. By analyzing by theprocedures as will be described below, this product was identified withtrimethyl(ethylcyclopentadienyl)platinum (C₂ H₅ C₅ H₄)Pt(CH₃)₃ which wasobtained in an amount of 48.0 mmol at a yield of 51%.

Identification

(1) Pt content: 57.5 wt. % (calculated: 58.52 wt. %).

(2) CH analysis: C 36.42 wt. % H 5.49 wt. % (calculated: C 36.03 wt. % H5.44 wt. %)

    ______________________________________    (3)    .sup.1 H-NMR           apparatus    BRUKER AC300P (300 MHz)           solvent      CDCl.sub.3           method       1D    ______________________________________    Spectrum and assignment    δ.sub.H (ppm)                proton  number                             assignment    ______________________________________    0.70-0.97   9H           3Me    1.14        3H           CH.sub.3 ;Et    2.32        2H           CH.sub.2 ;Et    5.32-5.54   4H           CH;cyclopentadienyl.    ______________________________________

Physical Properties and Purity

(4) Melting point: not higher than -78° C.

(5) Vapor pressure: 0.3 Torr at 50-55° C.

(6) Density: about 1.5 g/cm³.

(7) Viscosity: about 5 cP (room temperature)

(8) Reactivity: being stable without reacting with air or water.

(9) Heat stability: being stable at 150° C.

(10) TG-DTA:

Measurement conditions: Ar 1 atm., sample weight 10.10 mg, temperaturerise rate 10.0 deg/min. Results: wight loss began at about 30° C. andreached 50% and 100% respectively at 150° C. and 170° C.

(11) Purity

Analytical data of impurities (expressed in ppm) Fe 1, Al<1, Si 2, Na 1,Ca 2. Thus a high purity was observed.

EXAMPLE 2 Production of Pure Pt Film by the CVD Method with the Use ofTrimethyl(ethylcyclopentadienyl)platinum (C₂ H₅ C₅ H₄)Pt(CH₃)₃

The whole system involving a feedstock container and a thermaldecomposition reactor was maintained under atmospheric pressure. Thefeedstock container packed with 14 g oftrimethyl(ethylcyclopentadienyl)platinum (C₂ H₅ C₅ H₄)Pt(CH₃)₃ wasintroduced into a thermostatic chamber at 35° C. and a carrier gas Arwas bubbled thereinto at 20 sccm.Trimethyl(ethylcyclopentadienyl)platinum was evaporated together withthis gas and fed into the thermal decomposition reactor. At the sametime, 50 sccm of a hydrogen gas was fed into the thermal decompositionreactor provided therein with an Si substrate heated to 150 ° C. Thetrimethyl(ethylcyclopentadienyl)platinum was decomposed on thissubstrate to thereby form a pure Pt film of 40 nm in thickness after 20minutes. The obtained film was identified with metallic platinum by XRD.When the film was dissolved and ICP emission spectral analysis waseffected to detect metallic impurities, no metallic impurity was foundout.

The trimethyl(ethylcyclopentadienyl)platinum (C₂ H₅ C₅ H₄)Pt(CH₃)₃ ofthe present invention is in the form of a liquid at room temperature andhas a sufficient vapor pressure at around 35° C. Thus it can bequantitatively supplied by gas bubbling or with the use of a liquid massflow controller as a feedstock in the CVD method and thermallydecomposed on a substrate in a hydrogen atmosphere to give Pt films.According to the present invention, pure Pt films can be produced by theCVD method at a high mass-productivity.

What is claimed is:
 1. Trimethyl(ethylcyclopentadienyl)platinum.
 2. Aprocess for producing trimethyl(ethylcyclopentadienyl)platinum whichcomprises reacting iodotrimethylplatinum with sodiumethylcyclopentadienide in a solvent.
 3. A process for producingplatinum-containing films by the chemical vapor deposition method whichcomprises bringing a heated substrate into contact withtrimethyl(ethylcyclopentadienyl)platinum.